Nanoassembly methods for producing quasi-three-dimensional nanoarrays

ABSTRACT

Nanoassembly methods for producing quasi-3D plasmonic films with periodic nanoarrays of nano-sized surface features. A sacrificial layer is deposited on a surface of a donor substrate having periodic nanoarrays of nanopattern features formed thereon. A plasmon film is deposited onto the sacrificial layer and a dielectric spacer is deposited on the plasmon film. The donor substrate having the sacrificial layer, plasmon film, and dielectric spacer thereon is immersed in a bath of etchant to selectively remove the sacrificial layer such that the plasmon film and the dielectric spacer thereon adhere to the surface of the donor substrate. The dielectric spacer and the plasmon film are mechanically separated from the donor substrate to define a quasi-three dimensional (3D) plasmonic film having periodic nanoarrays of nano-sized surface features defined by the nanopattern features of the donor substrate surface. The quasi-3D plasmonic film is then applied to a receiver substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation patent application of co-pending U.S. patentapplication Ser. No. 17/126,316 filed Dec. 18, 2020, which claims thebenefit of U.S. Provisional Application No. 62/949,769, filed Dec. 18,2019. The contents of these prior applications are incorporated hereinby reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under contract numberFA8650-16-D-5403 awarded by the Air Force Research Laboratory (AFRL),and under Sponsor Award No. 1928784-CMMI awarded by the National ScienceFoundation. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

The present invention generally relates to quasi-three-dimensional(quasi-3D) nanoarrays. The invention particularly relates to assemblymethods for producing quasi-3D plasmonic films with periodic nanoarrayscomprising nano-sized surface features, wherein the methods involvelimited physical contact during the assembly process.

Interaction of incident light with quasi-3D plasmonic nanoarraysprovides capabilities to manipulate light at nanoscale lengths in waysthat cannot be obtained with conventional optics. Diverse types ofquasi-3D plasmonic nanoarrays with tailored feature shapes, sizes andconfigurations have been explored for a broad range of light-drivensensors and actuators, including imagers, light displays, biologicalsensors, lasers, and antennas.

Traditionally, the construction of quasi-3D plasmonic nanoarrays haslargely relied on the use of nanolithography techniques such aselectron-beam (e-beam) lithography, focused ion-beam lithography andinterference lithography, but their laborious, complex andtime-consuming nature impedes practical applications. In addition, thesenanolithography methods often require the use of thermal and chemicaltreatments, leading to additional increase of complexity and risk inprotecting the substrate materials.

Alternative strategies exploit advanced printing techniques such asnanoimprinting and modular transfer printing, allowing for deterministicintegration of quasi-3D plasmonic nanoarrays with a foreign receiversubstrate, and thereby circumventing the incompatibility of thenanolithography conditions with substrate materials. Nevertheless, thechoice of receiver substrate remains limited by the required physicalcontact forces during printing steps, yielding an increased risk ofpotential damages to several substrates composed of mechanically fragilematerials and structures.

In view of the above, though manipulation of light through nanoarrays of3D patterns provides unique opportunities to harness light, practicalimplementation has been hindered by a lack of effective methodology. Assuch, it would be desirable if methods were available for producingnanoarrays of quasi-3D plasmonic nanoarrays that were capable of atleast partly overcoming or avoiding the problems, shortcomings ordisadvantages noted above.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides nanoassembly methods suitable forproducing quasi-3D plasmonic films with periodic nanoarrays ofnano-sized surface features.

According to one aspect of the invention, a method is provided thatincludes providing a donor substrate comprising periodic nanoarrays ofnanopattern features formed on a surface thereof, depositing asacrificial layer on the surface of the donor substrate, depositing aplasmon film onto the sacrificial layer, depositing a dielectric spaceronto the plasmon film, immersing the donor substrate having thesacrificial layer, plasmon film, and dielectric spacer thereon in a bathof etchant to selectively remove the sacrificial layer such that theplasmon film and the dielectric spacer thereon adhere to the surface ofthe donor substrate, mechanically separating of the dielectric spacerand the plasmon film from the donor substrate to define a quasi-threedimensional (3D) plasmonic film that comprises the dielectric spacer andthe plasmon film and has periodic nanoarrays of nano-sized surfacefeatures defined by the periodic nanoarrays of nanopattern featuresformed on the surface of the donor substrate, and applying the quasi-3Dplasmonic film to a receiver substrate.

According to another aspect of the invention, a method is provided thatincludes providing two or more quasi-3D plasmonic films that may beproduced as described above, and then applied to a receiver substrate ina stacked configuration.

Technical effects of methods as described above preferably include theability to produce quasi-3D plasmonic films having periodic nanoarraysthereon with limited physical contact during the fabrication of thefilms on a donor substrate, thereby reducing the risk of damaging thedonor substrate and the plasmonic films.

Other aspects and advantages of this invention will be appreciated fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1H schematically represent certain steps of ananoassembly method for fabricating quasi-3D plasmonic films havingperiodic nanoarrays of nano-sized surface features in accordance withcertain nonlimiting aspects of the invention.

FIGS. 2A through 2C schematically represent a sequence of physicaldebonding and separation of a quasi-3D plasmonic film from a surface ofa donor substrate, wherein the surface of the donor substrate has aperiodic nanopattern of nanoholes and the resulting plasmonic film isformed to have complementary periodic nanoarrays of nano-sizednanoposts.

FIGS. 3A through 3D depict aspects of quasi-3D plasmonic films withperiodic nanoarrays of different types of nano-sized surface features.Each of FIGS. 3A through 3D includes a schematic representation of asingle nano-sized surface feature (left), an SEM image (middle column),and analysis of transmission spectra (right) of the quasi-3D plasmonicfilm thereof. The surface features shown are nanoposts (FIG. 3A),nanoholes (FIG. 3B), bilayer nanowire gratings (FIG. 3C), andring-shaped disks (FIG. 3D). Scale bars in the SEM images of FIGS. 3Athrough 3D are, respectively, 3.3 μm, 2.0 μm, 1.8 μm, and 2.0 μm fromthe top.

FIGS. 4A and 4B represent a schematic of a modeled structure (FIG. 4A)and FEA results of peeling strength (P)-debonding distance (d) curvesfor quasi-3D nanoposts in dry and wet conditions (FIG. 4B).

FIG. 5A contains images showing the progressive stacking of multipleplasmonic films having dissimilar quasi-3D nanoposts. Scale bar is 2.3μm. FIG. 5B contains images of nine plasmonic films having dissimilarquasi-3D nanoposts of different sizes and spacings. Scale bar is 3.3 μm.

FIG. 6 is an image showing a quasi-3D plasmonic film with periodicnanoarrays of nanoposts applied to a preexisting image detector. Scalebar is 4.5 mm.

FIG. 7A is a schematic representation of a nanohole formed in a donorsubstrate to be tapered by about 80° relative to the interior lowersurface of the nanohole, and FIG. 7B shows a cross-sectional SEM imageof a tapered nanohole having substantially the same taper as shown inFIG. 7A. Scale bar is 160 nm.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are quasi-3D nanoarrays, particularly quasi-3Dplasmonic films with periodic nanoarrays of nano-sized surface features,and nanoassembly methods for the fabrication of such quasi-3Dnanoarrays. As used herein, “nano-sized features” and “nano-sizedsurface features” are understood to refer to features having a maximumdimension of not more than 10 micrometers, a “nanoarray” is understoodto refer to a two-dimensional (2D) array of nano-sized features, and“quasi-3D” is understood to refer to a 3D structure with a thickness ofone nano-sized feature in the third (z) dimension. The nanoassemblymethods entail the fabrication of quasi-3D films including nano-sizedsurface features thereof on donor fabrication substrates (or simply“donor substrates”), intact separation of the quasi-3D films from theirdonor fabrication substrates, and subsequent transfer of the quasi-3Dfilms to a receiver substrate, as well as devices and systems thatutilize one or more of such quasi-3D films, as a nonlimiting example, tomanipulate light at nanoscale lengths. Unlike conventional approaches,the entire nanoassembly method may occur in distilled water at roomtemperature without the need of further chemical, thermal and mechanicaltreatments, allowing for the possibility of the donor fabricationsubstrates to be reused and/or the use of a wide variety of materials,structures, and devices as receiver substrates, as nonlimiting examples,wafers, preexisting electro-optical (EO) sensors, and other electronicdevices of interests.

Nonlimiting embodiments of the invention are described below inreference to experimental investigations leading up to the invention.

Nonlimiting process steps utilized by investigations leading to thepresent invention are schematically illustrated in FIGS. 1A through 1H.In the investigations, quasi-3D plasmonic films of periodic nanoarrayswere fabricated on silicon donor substrates that were each processed tohave a periodic nanoarray of nanopattern features in or on (in FIGS. 1Athrough 1H, recesses or nanoholes defined in) one of their surfaces.Nonlimiting examples of suitable methods for forming nanopatterns ondonor substrates include lithography techniques, for example, e-beam,interference lithography, photolithography, nanoimprint, focused ionbeam, etc. In FIGS. 1A through 1H, the nanopattern features 12 areschematically illustrated as recesses or nanoholes 12 defined in asurface 18 of a donor substrate (“Donor Si substrate”) 10. The quasi-3Dplasmonic films were fabricated on the nanopatterned donor substrates 10by first depositing a sacrificial nickel (Ni) layer 14 (about 10 nm) anda gold (Au) plasmon film 16 (about 50 nm) with an e-beam evaporator (notshown), such that the sacrificial layer 14 and the plasmon film 16 weredeposited within the nanoholes 12 and on the surface 18 of the donorsubstrate 10 (FIG. 1A). Though nickel was used as the sacrificial layer14 and gold was used as the plasmon film 16, the sacrificial layer 14and plasmon film 16 could be formed by a wide variety of other materialsknown to those skilled in the art, and such materials are within thescope of the invention, as nonlimiting examples, plasmon films formed ofaluminum, silver, etc. Thereafter, a dielectric spacer 20 was depositedon the surface of the plasmon film 16 by spin-coating (FIG. 1B). Thedielectric spacer 20 is identified in FIG. 1B as “PMMA” (poly(methylmethacrylate)), though the dielectric spacer 20 could be formed by awide variety of other dielectric materials known to those skilled in theart and such materials are within the scope of the invention, asnonlimiting examples, benzocyclobutene (BCB) and SU-8 (whose compositionis reported to be based on a multifunctional bisphenol A novolak epoxyresin and a photoacid generator as a curing agent). The entire structurewas immersed in a bath of a nitric acid aqueous solution (Nickel EtchTFB, Transene Company, Inc.) to exclusively remove the sacrificial layer14 beneath the plasmon film 16, allowing the remaining films (theplasmon film 16 and dielectric spacer 20) to sink and adhere on thesurface 18 of the silicon donor substrate 10 by van der Waals adhesiveforce (FIG. 1C). The resulting structure was then rinsed with distilledwater to keep the dielectric spacer 20 wet while its top surface waswiped to stay dry. A water-soluble tape 22 (“WST,” Aquasol Corporation)was then attached to serve as a temporary handling holder for theplasmon film 16 and dielectric spacer 20 (FIG. 1D). Mechanical peelingof the water-soluble tape 22 was performed at a constant rate using anautomated tool, resulting in intact separation from the donor substrate10 of a quasi-3D plasmonic film 24 formed by the plasmon film 16 anddielectric spacer 20, which together formed what may be referred to as ametal-dielectric composite (FIG. 1E). In the nonlimiting embodimentshown, the nanoholes 12 in the surface 18 of the donor substrate 10 hasresulted in the quasi-3D plasmonic film 24 comprising a periodicnanoarray of quasi-3D nano-sized surface features 26 in the form ofnanoposts that were shaped and sized complementary to the nanoholes 12,spaced laterally across the plasmonic film 24, and project in adirection generally normal to the bulk of the plasmonic film 24.Placement of the water-soluble tape 22 on the surface of water 28 atroom temperature (FIG. 1F) leads to complete dissolution of the tape 22,allowing the quasi-3D plasmonic film 24 to stay afloat on the surface ofthe water 28 (FIG. 1G).

FIG. 1H schematically represents a quasi-3D plasmonic film 24 fabricatedas described above as transferred to receiver substrate 30, as anonlimiting example, a double-side polished (DSP) silicon wafer. Forthis step in the investigation, the receiver substrates were immersed indistilled water (about 50 mL) contained in a petri dish on a probestation. Each receiver substrate was immersed beneath the water by adistance of less than 1 mm. A plasmonic film 24 was then floated on thewater surface and positioned and aligned with the receiver substrate 30using a micromanipulator (not shown) capable of full X-Y movements and360° rotation. Once the plasmonic film 24 was aligned with the receiversubstrate 30, water was slowly removed from the petri dish until theplasmonic film 24 settled onto the upper surface of the receiversubstrate 30, at which time the film 24 remained adhered to the surfaceof the substrate 30 via van der Waals force. Misalignment of a plasmonicfilm 24 with its receiver substrate 30 was corrected by soaking theplasmonic film 24 with water introduced at an angle of about 20° fromthe water surface, which caused the misaligned plasmonic film 24 to bereleased intact from the receiver substrate 30 by surface tension of thewater. Once a plasmonic film 24 was properly aligned and adhered to thesurface of a receiver substrate 30, the resulting structure was eitherdried at room temperature to secure the interfacial bonding with thereceiver substrate 30 or, if permitted by the receiver substrate 30, wasannealed to promote adhesion (FIG. 1H), as a nonlimiting example, at atemperature of about 60° C. for about 10 minutes in a convection oven.Testing of interfacial adhesion evidenced that annealing was capable ofincreasing adhesion strength of a plasmonic film 24 to the surface of areceiver substrate 30 by more than 50% as compared to the interfacialadhesion achieved at room temperature.

FIGS. 2A through 2C are schematic illustrations depicting the physicalseparation of a quasi-3D plasmonic film 24 from a donor substrate 10that was fabricated to have a periodic nanoarray of nanopattern features12 in or on (in this embodiment, recesses or nanoholes defined in) oneof its surfaces. FIGS. 2A through 2C generally correspond to FIGS. 1B,1C, and 1D, respectively. By modifying the form of the nanopatternfeatures 12 formed on the surface of a donor substrate 10, quasi-3Dplasmonic films with periodic nanoarrays comprising various forms ofsurface features 26 are within the scope of the invention.

FIG. 3A includes a schematic representation of a nanopost (left), ascanning electronic microscope (SEM) image of a quasi-3D plasmonic filmhaving an nanoarray of nanoposts (middle), and experimental and modelingresults of transmission spectra measurements obtained with a Fouriertransform infrared (FTIR) spectrometer (Nicolet 5700) and a ComputerSimulation Technology Microwave Studio (CST-MWS) based on a finiteintegration technique (FIT) (right). FIGS. 3B, 3C, and 3D similarlyinclude schematic representations, SEM images, and experimental andmodeling transmission spectra measurements of quasi-3D plasmonic filmshaving periodic nanoarrays of, respectively, nanoholes, gratings, andring-shaped disks. Examination with SEM and optical imaging oftransferred quasi-3D plasmonic films on their receiver substratesevidenced no visual defects or damage. Repetitive transmission spectrameasurements at widely spread locations on these nanoarrays producedconsistent outcomes, highlighting the uniform integrity of thenano-scaled features over the surfaces of the films. Following removalof the plasmonic films, optical images in their silicon donor substratesconfirmed the integrity of the donor substrates, evidencing theirability to be reused as a cost-saving factor.

FIGS. 4A and 4B represent a schematic of a modeled structure (FIG. 4A)and exemplary finite element analysis (FEA) results of peeling strength(P) versus debonding distance (d) curves for quasi-3D plasmonic films 24with periodic nanoarrays of nanoposts 26 (e.g., FIG. 3A) in dry (20%relative humidity) and wet (water) conditions (FIG. 4B). The interfacialseparation between the quasi-3D plasmonic films 24 and their silicondonor substrates 10 under wet conditions occurred by overcoming the wetadhesion of confined water molecules between the plasmon films 16 andthe surfaces of the silicon donor substrates 10 from which thesacrificial layer 14 had been completely removed. Experimental and FEAresults of debonding load-displacement (d) curves of 1×1 cm² quasi-3Dplasmonic films (50 nm Au plasmon film with a 1 μm PMMA dielectricspacer) with periodic nanoarrays of nanoposts 26 under dry and wetconditions consistently evidenced that the debonding load (L) rapidlyincreased within about 1 mm of an edge of the film 24, and thendecreased until becoming generally constant to a steady state load(L_(ss)). Notably, a substantial decrease in L_(ss) of more than about70% occurred under wet conditions as compared with dry conditions,indicating that the presence of water resulted in the reduction ofinterfacial energy at the 3D nanotextured surfaces of the plasmonicfilms 24.

Experimental, computational (FEA), and theoretical results revealed theeffect of the height, H_(post), of a nanopost on L_(ss). The resultsindicated that the steady state debonding load per unit width (L_(ss)/b)increased with increasing H_(post) from 200 nm to 400 nm, which wasattributed to the increased deformation energy required for longernanoposts. In theory, the energy balance of quasistatic interfacialdebonding can be expressed as: W_(L)=W_(interface)+W_(deformation),where W_(L) (=L_(ss)·ΔD) is the work done by the L_(ss) and ΔD is thedebonding displacement; W_(interface) (=G·b·ΔD) is the interfacialadhesion energy between a plasmonic film and silicon donor substrate,where G is the adhesion energy per unit area at the interface;W_(deformation) (u·b·ΔD·H_(post)) is the deformation energy from thequasi-3D nanoposts, where U is the deformation energy density. As aconsequence, the energy balance can be further written as:L_(ss)/b=G+u·H_(post), wherein G and u are independent of the H_(post)because both the interface and materials properties of the quasi-3Dnanoposts remain unchanged. These assessments were consistent with thefindings that L_(ss) under wet conditions was substantially less thanunder dry conditions for the same H_(post), mainly due to the reducedinterfacial adhesion energy by the effect of water molecules.Evaluations of similar quasi-3D Au/PMMA plasmonic films but configuredwith periodic nanoarrays of nanoholes (e.g., FIG. 3B) producedconsistent results to support and confirm these findings.

Modeling (FEA) results revealed that the underlying strain distributionof the plasmonic film during the interfacial debonding process under dryand wet conditions. The modeled structure included a unit of Au (50nm)/PMMA (1 μm) plasmonic film configured with quasi-3D nanoposts(H_(post)=300 nm) and nanoholes (H_(hole)=300 nm). The results revealedthat the maximum principal strain (ε_(max)) appeared in the PMMAdielectric spacer where the magnitude in the wet condition was more than60% less than that in the dry condition. This aspect allowed theplasmonic film to experience insignificant mechanical constraints duringthe interfacial debonding process and thereby was able to reduce thepotential risk of defects, as also consistent with the above-mentionedexperimental observations. Modeling was also performed for variedH_(post) and H_(hole) as well as different dielectric spacers such asBCB and SU-8 under dry and wet conditions.

The ability to assemble several identical or different types of quasi-3Dplasmonic films in a spatially controlled manner provides a mean ofattaining advanced light manipulation. FIG. 5A contains SEM imagesdepicting the progressive application of quasi-3D plasmonic films withperiodic nanoarrays of nanoposts to create a multilayered plasmonic filmstack 32. The relative alignment error of each stacked film was below 1μm, which can be further improved by employing alignment marks. Thenanoposts of the plasmonic films seen in FIG. 5A were similar in termsof diameters (D_(post) of about 1.0 μm) and spacings (G_(edge) of about0.4 μm), though stacking of plasmonic films with dissimilar nanoposts orwith smaller and greater diameters and spacings is also within the scopeof the invention. As a nonlimiting example, FIG. 5B represents plasmonicfilms formed with dissimilar nanoposts in terms of different diameters(D_(post) of about 1.0 μm to about 2.3 μm) and spacings (G_(edge) ofabout 0.6 μm to about 1.6 μm). The plasmonic films of FIG. 5B weresequentially transferred from a silicon donor substrate to a receiversubstrate (a DSP wafer) loaded on a temporary handling holder. Adhesionat the interface between each transferred plasmonic film was secured bya post-annealing treatment in a convention oven at, for example, 60° C.for 10 minutes. The SEM images shown in FIG. 5B and correspondingtransmission spectra measurements indicated that no defects occurredthroughout the multiple stacking process. These investigationshighlighted the spatial controllability and modular capability of thenanoassembly method descried herein, evidencing its suitability for usein surface plasmon applications.

FIG. 6 is an optical image of an individual quasi-3D plasmonic film 24produced and applied to a preexisting electro-optical (EO) sensor 40 bya nanoassembly method of this invention. A hybrid pixel detector (HPD)34 served as the receiver substrate. Basic components of the HPD 34included GaSb for contacts, InAs/GaSb/InSb for active (×300layers)/bottom (×80 layers) superlattice and indium (In) bumps forconnections, all assembled with a silicon fan-out chip 38 through aflip-chip-on-laminate process. The materials and structures of the HPD34 represent a chemically and mechanically vulnerable receiver substratethat is otherwise difficult to directly construct quasi-3D plasmonicfilms by conventional nanofabrication technologies.

The assembly process used to construct the sensor 40 began by mountingand wire-bonding the HPD 34 to a leadless chip carrier (LCC) 36 tocharacterize device performance (spectral response, photocurrent, anddark current, etc.). The LCC 36 also served as a temporary handlingholder that allowed the HPD 34 to avoid any physical contact during theentire process. The resulting structure was then immersed in water whilethe quasi-3D plasmonic film 24 (Au (50 nm)/PMMA (800 nm), 1×1 cm²)configured with nanoposts (H_(post)=0.2 μm, D_(post)=1 μm, G_(edge)=1μm) was afloat on the water surface. Subsequent alignment took place ona probe station with full X-Y movements and 360° rotation undermicroscope examination. Drying of the fully assembled unit occurred atroom temperature. Microscope and SEM examination of the completed sensor40 evidenced no damage or defects to the HPD 34.

Post-analysis occurred in a custom setup that allowed for theacquisition of optical-to-electrical measured spectral responses at 77K.The results showed that distinct oscillatory characteristics appeared inall of the spectral responses, which was attributed to the Fabry-Perotcavity resonances between air and the embedded mirror planes consistingof ohmic contact under the In bump metallization. Light transmittedthrough narrow gaps of the nanoposts of the quasi-3D plasmonic film 24exhibited waveguide resonance behaviors that were correlated tointeractions between the embedded plasmonic layers where the maximumvalue of |E| occurs at the peak wavelength. Spectral responses after theremoval of the plasmonic film 24 remained substantially unchanged fromresponses of the as-fabricated HPD 34 within the range of measurementerror, providing additional evidence that the HPD 34 remained intacteven after the assembly and removal of the plasmonic films 24. Dark- andphoto-currents were obtained at 77K and at applied bias voltages rangingfrom −500 mV to 0 V for the as-fabricated HPDs 34 and after removal ofthe plasmonic films 24 from the HPDs 34. The dark- and photo-currentsunderwent negligible changes within the range of measurement error,which confirmed that the intrinsic performance of the HPD 34 waspreserved without any degradation.

The investigations described above represent development of ananoassembly method that can occur under wet condition, enablingdefect-free integration of various quasi-3D plasmonic films with areceiver substrate. Notably, aside from the use of water and roomtemperature conditions, the entire nanoassembly method did not requireany chemical or thermal treatments or require any physical contactforces other than van der Waals contact, which expands the types ofreceiver substrates that can be used by the method to essentiallyencompass arbitrary materials and structures. The advanced features ofmultiple modular assemblies in an either lateral or verticalconfiguration, taken together with the implementation of a set ofequipment for the interfacial debonding and the subsequent alignmentsteps, suggest the controllability and repeatability of the disclosednanofabrication process. The constituent quasi-3D composite materialsand structures presented herein are not the only options that can beachieved by this approach, and broad considerations of even more complex3D nanostructures or nanoelectronics are foreseeable. The resultingdevices utilizing the plasmonic films produced with the nanoassemblymethod illustrated the feasibility and utility in deterministicmanipulation of a light spectrum, providing the potential for expandingthe detection functionalities beyond conventional standards, forexample, for enhanced target detection via multispectral andhyperspectral imaging.

For the fabrication of the silicon donor substrates 10 described above,a conventional e-beam lithography technique was performed on siliconsubstrates to produce various periodic nanopatterns in a photoresistlayer. A thin layer (20 nm) of chromium formed by e-beam evaporator wasused to serve as a selective masking layer for subsequent etching of thesilicon donor substrates 10 by an anisotropic CF₄/O₂ plasma reactive ionetch (RIE). For the silicon donor substrates 10 formed to havenanopattern features 12 in the form of ring-shaped disks, a slightlylateral undercut-wet-etch process was added, followed by an e-beamevaporation to deposit another layer of chromium, wherein the subsequentlift-off process resulted in forming coaxial aperture arrays. For othertypes of silicon donor substrates 10, a brief isotropic etching was usedto slightly taper the sidewalls of the nanopattern features 12 in thedonor substrates 10, by about 80° from the bottom of the features 12,providing a passage for solutions (water or etching solution) to passthrough efficiently (FIGS. 7A and 7B). Finally, the chromium maskinglayer was removed by immersion in a bath of a chromium etchant tocomplete the entire process.

For transmission spectra analysis, both arrays of the nanoposts andnanoholes were conceptually considered as two plasmonic layers ofmetallic hole array (MHA) and metallic disk array (MDA) separated by aspacer layer, along with the PMMA atop (giving rise to improving thetransmission due to the Fabry-Perot cavity resonance). The waveguide(WG) resonance mode through the nanogaps formed by the periodicnanoarrays was ascribed to the interaction between MDA and MHA layers,resulting in greatly enhancing the transmission (EOT, extraordinaryoptical transmission) and realizing practical, easy-to-control opticalfilter (due to the ease of tuning the full-width at half-maximum and thepeak wavelength by geometrical parameters, e.g., grating period,diameter, nanopost height, nanohole depth). These arrays could be ofuseful for many sensing techniques, termed algorithmic spectrometrybecause the suitable spectral shape of sensor's responsivities can becreated by the deterministic integration of precisely engineeredperiodic nanoarrays with preexisting EO sensors to provide desiredspectral filter shapes.

For example, periodic nanoarrays of nanowire gratings (FIG. 3C) could beused to polarize light by transmitting only a specific polarizationstate, i.e., only passing through light oscillating perpendicular to themetallic nanowires (p-polarized light). Such nanoarrays could providethe advantages of lowering the s-polarized transmission by using twoself-aligned nanowire gratings, as compared with traditionalone-dimensional metallic gratings (planar grating layer) and increasingthe p-polarized transmission due to the Fabry-Perot cavity resonance inthe dielectric spacer. The extinction ratio used as the performanceindicator of a nanowire grating (which is given by the base-10 logarithmof the ratio of the p- and s-polarized transmission) was found to beabout 15 dB at 7.55 μm with a high p-polarized transmission of 89%. InFIG. 3C, the number of distinct dips can be clearly seen around about3.4 μm, 5.8 μm, 7 μm, and 8-9 μm, which were attributed to the PMMAabsorption itself, specifically C—H bond stretching vibrations, thepresence of the acrylate carboxyl group, the bending vibration of theC—H bonds, and C—O—C stretching vibration, respectively.

The last example among the representative arrays is the Au deposited ona hollow cylinder of PMMA (FIG. 3D), which was designed to isolate awide spectral band and to exhibit a high peak transmission in thepassband. The characteristic of plasmonic based bandpass filter can beeasily modified with changing the geometric parameters, e.g., inner andouter radii, height of PMMA hollow cylinder, dielectric material, etc.

While the invention has been described in terms of specific orparticular embodiments and investigations, it should be apparent thatalternatives could be adopted by one skilled in the art. For example,quasi-3D plasmonic films of types as described above and devices andsystems comprising such films could differ in appearance andconstruction from the embodiments described herein and shown in thedrawings, process parameters such as temperatures and durations could bemodified, and appropriate materials could be substituted for thosenoted. Accordingly, it should be understood that the invention is notnecessarily limited to any embodiment described herein or illustrated inthe drawings. It should also be understood that the phraseology andterminology employed above are for the purpose of describing thedisclosed embodiments and investigations, and do not necessarily serveas limitations to the scope of the invention. Therefore, the scope ofthe invention is to be limited only by the following claims.

The invention claimed is:
 1. A method of mechanically separating a quasithree-dimensional plasmonic film from a donor substrate comprisingnanopattern features on a surface thereof, the method comprising:providing the donor substrate with a sacrificial layer on the surface ofthe donor substrate, a plasmon film on the sacrificial layer, and adielectric spacer on the plasmon film; removing the sacrificial layerfrom the donor substrate in a bath of etchant; and separating thedielectric spacer and the plasmon film from the donor substrate todefine the quasi three-dimensional plasmonic film, the separating stepcomprising: applying a water-soluble tape material to the dielectricspacer of the quasi three-dimensional plasmonic film so that the tapematerial is attached thereto; using the tape material to cause intactseparation from the donor substrate of the quasi three-dimensionalplasmonic film and the tape material attached thereto; and removing thetape material from the dielectric spacer by contacting the tape materialwith water for a time sufficient to dissolve the tape material such thatthe quasi three-dimensional plasmonic film floats on a surface of thewater.
 2. The method of claim 1, wherein the water is distilled water.3. The method of claim 1, wherein the water is at room temperature. 4.The method of claim 1, wherein the removing of the sacrificial layerfrom the donor substrate causes the plasmon film and the dielectricspacer to adhere to the surface of the donor substrate by van der Waalsadhesive force.
 5. The method of claim 4, wherein the intact separationfrom the donor substrate of the quasi three-dimensional plasmonic filmand the tape material attached thereto comprises overcoming wet adhesionof confined water molecules between the plasmon film and the surface ofthe donor substrate.
 6. The method of claim 1, wherein the step ofremoving the tape material comprises placing the quasi three-dimensionalplasmonic film and the tape material attached thereto on the surface ofthe water.
 7. The method of claim 1, further comprising applying thequasi three-dimensional plasmonic film to a receiver substrate by:immersing and anchoring the receiver substrate in a quantity of waterunder the quasi three-dimensional plasmonic film; reducing the quantityof water until the quasi three-dimensional plasmonic film contacts asurface of the receiver substrate; and drying the receiver substrate andquasi three-dimensional plasmonic film to bond the quasithree-dimensional plasmonic film to the receiver substrate.
 8. Themethod of claim 7, further comprising adjusting the position of thequasi three-dimensional plasmonic film while afloat on the water overthe receiver substrate.
 9. The method of claim 8, further comprisingcorrecting any misalignment between the quasi three-dimensionalplasmonic film and the receiver substrate after contact therebetween bysoaking the receiver substrate in the water such that the quasithree-dimensional plasmonic film is released intactly from the receiversubstrate by surface tension of the water.
 10. The method of claim 1,wherein the donor substrate is a silicon substrate.
 11. The method ofclaim 1, wherein the plasmon film is a metal.
 12. The method of claim11, wherein the plasmon film comprises gold, silver, or aluminum. 13.The method of claim 1, wherein the dielectric spacer comprisespoly(methyl methacrylate) (PMMA), benzocyclobutene (BCB), or amultifunctional bisphenol A novolak epoxy resin.
 14. The method of claim1, wherein the quasi three dimensional plasmonic film has periodicnanoarrays of nano-sized surface features defined by periodic nanoarraysof nanopattern features on the surface of the donor substrate.